3GPP Long Term Evolution, LTE, is the fourth-generation mobile communication technologies standard developed within the 3rd Generation Partnership Project, 3GPP, to improve the Universal Mobile Telecommunication System, UMTS, standard to cope with future requirements in terms of improved services such as higher data rates, improved efficiency, and lowered costs. In a typical cellular radio system, wireless devices or terminals also known as mobile stations and/or user equipment units, UEs, communicate via a radio access network, RAN, to one or more core networks. The Universal Terrestrial Radio Access Network, UTRAN, is the radio access network of a UMTS and Evolved UTRAN, E-UTRAN, is the radio access network of an LTE system. The work of specifying the Evolved Universal Terrestrial Radio Access Network, E-UTRAN consisting of the Long Term Evolution, LTE, and System Architecture Evolution, SAE, concepts is currently ongoing within the 3rd Generation Partnership Project, 3GPP.
In an UTRAN and an E-UTRAN, a wireless device, also known as a User Equipment, UE, is wirelessly connected to a Radio Base Station, RBS. An RBS is a general term for a radio network node capable of transmitting radio signals to a wireless device and receiving signals transmitted by a wireless device. A logical node, commonly referred to as a NodeB, NB, in UMTS, and as an evolved NodeB, eNB or eNodeB, in LTE, is responsible for all radio-related functions in one or several cells. In the radio access network, control messages for connection setup, mobility and security are originating from the Radio Resource Control, RRC, located in the logical node, eNB, of a radio base station, RBS. In the following disclosure wireless device and UE will be used interchangeably to denote entities capable of wireless connection to a radio base station. Similarly, radio base station, RBS, and eNB will be used interchangeably to denote the access point to the radio access network.
The RRC is responsible for handling the radio access network-related procedures, including connection management, setting up bearers and mobility within the network. This includes establishing an RRC context, i.e. configuring the parameters necessary for communication between a wireless device and the radio access network, RAN.
In LTE a wireless device can be in two different states RRC_CONNECTED and RRC_IDLE. During the state RRC_IDLE, the wireless device does not belong to a specific cell. No data transfer takes place and the wireless device is inactive most of the time in order to maintain low power consumption. During the state RRC_CONNECTED, configuration information for the wireless device, i.e. the parameters necessary for communication between the wireless device and the radio access network, are known to both entities. Data transfer to/from the wireless device is possible only when there is an RRC connection during the state of RRC_CONNECTED.
In case of radio link failure, data transfer to/from a wireless device is disabled. Following radio link failure, there is a need for a quick recovery of the data transfer.